Better late then never, but hey at least it's only one day off. Yesterday was Twitter's five year anniversary of the first tweet sent on March 21, 2006 by co-founder Jack Dorsey. This was back when Twitter was known as just "Twttr."
Twitter's small team of the time had been busy brainstorming and programming for eight days before the platform was ready for its first non-automated message, which read "Inviting coworkers," according to Dorsey.
Twitter now handles an average of 140 million tweets a day, and the Twitter staff is over 400 people, according to the Twitter Blog. I'm sure you can still take part in the celebration by tweeting #TwitterMemory.